In this proposal we will investigate the biosynthesis of Rauscher murine leukemia virus (RLV) structural proteins in whole cells and cell-free systems. Antiserum to RLV structural proteins specifically precipitates virion proteins and large molecular weight precursor-like polypeptides from cellular extracts. The use of such specific immune probes combined with fractionation by SDS polyacrylamide gel electrophoresis allows isolation and quantitation of these polypeptides. Our results suggest that RLV internal structural proteins are made by way of large molecular weight precursor polypeptides. Another phase of the project concerns the translation of RLV subunit RNA and 65S RLV RNA in S-30 extracts derived from mouse cells and wheat germ. The mouse S-30 extracts synthesize two classes of high molecular weight polypeptides (125,000-150,000 daltons and 60,000-80,000 daltons), in response to 65S RLV RNA, which are immune precipitable by antiserum prepared against disrupted RLV particles. We plan to compare the polypeptides made in response to RLV subunit RNA and 65S RLV RNA by SDS polyacrylamide gel electrophoresis, by tryptic mapping procedures and by precipitation with antisera prepared against internal structural RLV proteins (i.e. p30, p16, and p14). The product made in the heterologous wheat germ S-30 extract from both RLV subunit RNA and 65S RNA will be examined by similar techniques and compared to that synthesized in homologous mouse S-30 extracts. The initiation dipeptide(s) and oligopeptide(s) coded by RLV subunit RNA will be synthesized in wheat germ S-30 extracts, and their sequence(s) determined to indicate the ploidy of RLV subunit RNA. Intracellular viral specific mRNAs will be partially purified and translated in S-30 extracts. Immune precipitation with antisera to viral proteins will be used to specifically isolate the polypeptide product made in response to RLV-specific mRNA fractions. The immune precipitable polypeptides will be characterized by tryptic digestion and fingerprinting techniques. The viral polypeptides encoded in the virion RNA and intracellular viral mRNA will be compared.